Additivity Rule of the Partial Molal Volume. 4. Its Proof Based on the Postulate of Independent Volume Changes for Unit Reactions

1988

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The effect of pressure was studied on the dimerization reactions of six di‐ and tri‐substituted nitrosobenzenes in carbon tetrachloride at 25°C. The obtained configurational volume changes for the prototype one bond formation reactions are in the range of —17 to —21 cm3 mol−1 at 6.13 MPa. The volume changes were interpreted in terms of the perturbation theory of liquid; they were dominated by the volume change in the reference system composed of hard spheres. Small differences between the observed and theoretical reference volume changes were ascribed to the perturbation due to electrostatic interactions between the solute and solvent; the perturbation volume changes were estimated by the Kirkwood theory of dipolar solvation.

Pressure Effect on Dimerization Equilibria of a Series of Substituted Nitrosobenzenes in Solution

1988

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Activation Volume for Dimerization Reaction of 2,4,6‐Trimethylnitrosobenzene in Solution

1988

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The effect of pressure on the rate and equilibrium constants for the dimerization reaction of 2,4,6‐trimethylnitrosobenzene in acetonitrile was studied up to 196 MPa at 25°C in order to examine whether the dynamical effect on the reaction process in solution can be neglected as assumed in the transition state theory. All the rate constants relevant to the dimerization were determined by the pressure relaxation method. The configurational reaction volume for the dimerization and the activation volume for the dissociation were —17.4 ± 0.7 and + 5.1 ± 0.3 cm3 mol 1 at 98 MPa, respectively. The experimental results were in reasonable agreement with the theoretical ones that were calculated for the model system composed of hard spheres according to the liquid theory and the transition state theory. The dynamical effect on the activation volume was not detected in the present reaction system.

Volume Profile of the Reversible Dimerization Reaction of 2‐Methyl‐2‐nitrosopropane: Validity of the Hard Sphere Fluid Model and the Transition State Theory

Kimura

1988

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The volume profile of the reversible dimerization reaction of 2‐methyl‐2‐nitrosopropane in carbon tetrachloride was determined at 25.0°C on the basis of the study of the pressure effect and the measurement of the solution density at 0.1 MPa. For the dissociation process, the configurational reaction volume was +30.3 ± 0.8 cm3 mol−1 and the apparent activation volume was +7.7 ± 0.3 cm3 mol−1 at 25.0°C and 61.3 MPa. The configurational reaction volume at 0.1 MPa was estimated as +36 cm3 mol−1 from the high pressure study in agreement with the result of the density measurement. The experimental values of the reaction and activation volumes were successfully reproduced by using the hard sphere fluid model. The agreement of experiment and theory indicates that the hard sphere fluid model is valid for describing the volume change for the molecular reaction, and implies that the transition state theory (TST) is valid for interpreting the pressure dependence of the rate constant. A simple illustration of the validity of TST is presented; the energy relaxation process plays a key role in determining the validity.